Inner hole machining using laser machining is performed by setting a machining start point in a portion that is cut off as a waste, and emitting laser light to cut through the waste, starting from the machining start point, toward a part to be an edge of a through hole and follow the edge.
In laser machining, the cut slot, while it is thin, has a certain thickness and a force is applied to the material to be cut due to the pressure of the gas ejected from the machining nozzle; therefore, when inner hole machining is performed, the waste side comes off at the timing before the nozzle reaches the machining path end. Consequently, there is a problem in terms of quality that laser light irradiation becomes excessive near the machining end due to redundant laser light irradiation and this leads to discoloration of the end portion.
The slot width during laser machining changes due to the effects of, for example, the set cutting conditions and the ambient environment; therefore, it is difficult to always maintain a constant slot width. Consequently, it is not possible to create an NC program such that laser irradiation is stopped at the timing when the waste comes off.
Patent Literature 1 discloses a technology for detecting that laser machining is approaching the end point of the cutting portion by using, for example, a proximity sensor at the tip of the nozzle.
Patent Literature 2 discloses a technology for invalidating an anomaly detection signal so that machining does not stop near the machining end point.